Heresy is defined as deviation from orthodoxy. This definition steers from bias towards any particular sect or denomination. Protestants can argue back that the Catholic church is heretical for perverting original teachings of the church. Vice - Versa.

In my opinion, some 'heretics' are harmless and inconsequential if viewed within the context of salvation. Eg. I disagree with Monophysitism, but by no means think that they;re goin to hell for their views or anything, its inconsequential.